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SubjectRe: [PATCH 3/5] virtio: Don't expose legacy net features when VIRTIO_NET_NO_LEGACY defined.
On Fri, Feb 06, 2015 at 03:36:54PM +1030, Rusty Russell wrote:
> In particular, the virtio header always has the u16 num_buffers field.
> We define a new 'struct virtio_net_modern_hdr' for this (rather than
> simply calling it 'struct virtio_net_hdr', to avoid nasty type errors
> if some parts of a project define VIRTIO_NET_NO_LEGACY and some don't.
>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> ---
> include/uapi/linux/virtio_net.h | 30 ++++++++++++++++++++++++++++--
> 1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> index b5f1677b291c..32754f3000e8 100644
> --- a/include/uapi/linux/virtio_net.h
> +++ b/include/uapi/linux/virtio_net.h
> @@ -35,7 +35,6 @@
> #define VIRTIO_NET_F_CSUM 0 /* Host handles pkts w/ partial csum */
> #define VIRTIO_NET_F_GUEST_CSUM 1 /* Guest handles pkts w/ partial csum */
> #define VIRTIO_NET_F_MAC 5 /* Host has given MAC address. */
> -#define VIRTIO_NET_F_GSO 6 /* Host handles pkts w/ any GSO type */
> #define VIRTIO_NET_F_GUEST_TSO4 7 /* Guest can handle TSOv4 in. */
> #define VIRTIO_NET_F_GUEST_TSO6 8 /* Guest can handle TSOv6 in. */
> #define VIRTIO_NET_F_GUEST_ECN 9 /* Guest can handle TSO[6] w/ ECN in. */
> @@ -56,6 +55,10 @@
> * Steering */
> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */
>
> +#ifndef VIRTIO_NET_NO_LEGACY
> +#define VIRTIO_NET_F_GSO 6 /* Host handles pkts w/ any GSO type */
> +#endif /* VIRTIO_NET_NO_LEGACY */
> +
> #define VIRTIO_NET_S_LINK_UP 1 /* Link is up */
> #define VIRTIO_NET_S_ANNOUNCE 2 /* Announcement is needed */
>
> @@ -71,8 +74,9 @@ struct virtio_net_config {
> __u16 max_virtqueue_pairs;
> } __attribute__((packed));
>
> +#ifndef VIRTIO_NET_NO_LEGACY
> /* This header comes first in the scatter-gather list.
> - * If VIRTIO_F_ANY_LAYOUT is not negotiated, it must
> + * For legacy virtio, if VIRTIO_F_ANY_LAYOUT is not negotiated, it must
> * be the first element of the scatter-gather list. If you don't
> * specify GSO or CSUM features, you can simply ignore the header. */
> struct virtio_net_hdr {
> @@ -97,6 +101,28 @@ struct virtio_net_hdr_mrg_rxbuf {
> struct virtio_net_hdr hdr;
> __virtio16 num_buffers; /* Number of merged rx buffers */
> };
> +#else /* ... VIRTIO_NET_NO_LEGACY */
> +/*
> + * This header comes first in the scatter-gather list. If you don't
> + * specify GSO or CSUM features, you can simply ignore the header.
> + */
> +struct virtio_net_modern_hdr {
> +#define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* Use csum_start, csum_offset */
> +#define VIRTIO_NET_HDR_F_DATA_VALID 2 /* Csum is valid */
> + __u8 flags;
> +#define VIRTIO_NET_HDR_GSO_NONE 0 /* Not a GSO frame */
> +#define VIRTIO_NET_HDR_GSO_TCPV4 1 /* GSO frame, IPv4 TCP (TSO) */
> +#define VIRTIO_NET_HDR_GSO_UDP 3 /* GSO frame, IPv4 UDP (UFO) */
> +#define VIRTIO_NET_HDR_GSO_TCPV6 4 /* GSO frame, IPv6 TCP */
> +#define VIRTIO_NET_HDR_GSO_ECN 0x80 /* TCP has ECN set */
> + __u8 gso_type;
> + __virtio16 hdr_len; /* Ethernet + IP + tcp/udp hdrs */
> + __virtio16 gso_size; /* Bytes to append to hdr_len per frame */
> + __virtio16 csum_start; /* Position to start checksumming from */
> + __virtio16 csum_offset; /* Offset after that to place checksum */
> + __virtio16 num_buffers; /* Number of merged rx buffers */
> +};
> +#endif /* ...VIRTIO_NET_NO_LEGACY */

This kind of masks the fact that it's the same as
virtio_net_hdr_mrg_rxbuf. So it's forcing people to duplicate
code for transitional devices.

How about
struct virtio_net_modern_hdr {
struct virtio_net_hdr_mrg_rxbuf hdr;
}


This will also make it look nicer when we start
adding stuff in the header, the main header
is separated in a struct by its own, so it's
easy to apply operations such as sizeof.


> /*
> * Control virtqueue data structures
> --
> 2.1.0


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